Sunderland finally severed their ties with Ndong at the start of this week.
Sunderland have given their midfielder Didier Ndong notice under his contract.
Ndong's termination could save Sunderland in excess of £4 million.
Didier Ndong has been at Sunderland since the summer of 2016.
Sunderland midfielder Didier Ndong is reportedly wanted by Benfica.
Sunderland midfielder Didier Ndong never did get the move away from the Stadium of Light.
Sunderland did not manage to get rid of want-away duo Didier Ndong and Papy Djilobodji this summer.
Primeira Liga giants SL Benifca were reportedly in talks to sign Didier Ndong from League One Sunderland.
Ndong is expected to leave Sunderland this summer.
Sunderland have had an excellent summer transfer window, but still need to get rid of Papy Djilobodji and Didier Ndong to complete it.